Morning Edition

Listen Live

Next

BBC Newshour

In-depth analysis and commentary on today's biggest news stories as only the BBC can deliver. BBC "Newshour" covers everything from the growth of democracy to the threat of terrorism with a fresh, clear perspective from across the globe.

Why smell is so closely connected to our memories and emotions

Scent has the almost magical ability to transport us back to a specific time and place with one sniff. The holiday season is rife with these aromas: Pine takes us back to a cut-your-own Christmas tree farm of our youth, fresh sugar cookies recall afternoons in grandma’s kitchen, spiced cider reminds us of holiday parties.

Outside of the holidays, an old boyfriend or girlfriend’s perfume will always be attached to that long-ago ex.

So why is smell, more than other senses, so good at sending us spinning back in time?

“We know that people often report that smells are particularly evocative in bringing back memories, often from childhood,” said Pamela Dalton, a researcher at the Monell Chemical Senses Center in Philadelphia.

Dalton said one reason smell is so tightly interwoven with memory is because of how olfactory signals are processed.

First, scent molecules are sniffed into our noses and make contact with our olfactory receptors, which are located high up in the nasal cavity, behind the bridge of the nose.

The scent molecules bind to those olfactory receptors in a specific pattern. Once that pattern is formed, that signal is sent to the brain, where it is processed first by the primary olfactory cortex.

“Odors are processed a little bit differently than the other sensory systems, because all other sensory systems are routed through a structure in the brain called the thalamus, which is sort of like a gatekeeper,” Dalton said.

Smell bypasses the thalamus, which Dalton calls the ‘consciousness detector.’

“(It goes) directly to the primary olfactory cortex, and that may be why we experience odors in a different way than we do other kinds of sensory stimuli,” Dalton said.

Because scent skips the thalamus, smells can enter our brains and attach to memories without us consciously registering or processing them. Research shows smell is the only sense that is active even while we sleep, or are in a coma.

A matter of proximity

Another reason odors seem to be so tightly associated with emotional memories is due to brain structure.

“This olfactory area that processes the information is very close (in) proximity to a part of the brain that processes emotional information, and in particular emotional memories: the limbic system and the hippocampus and the amygdala,” Dalton said.

These structures are nestled near the center of the brain, and they developed together in our evolutionary ancestors. Dalton said smell was designed to immediately send an emotional signal: good or bad, approach or retreat, eat or avoid.

Fuzzy language leads to emotional responses

A third factor in this memory-triggering phenomenon, Dalton said, lies outside the brain, and has to do with language.

My olfactory time machine, the scent that always means ‘Christmas’ to me, is the incense Catholic priests burn at the altar on some holidays. Whenever the sticky-sweet scent hits my nostrils, I am transported back to the midnight masses of my youth: the drama of the Christmas story read from the pulpit, the glow of candles lighting the church, and the giddy anticipation of opening presents the next morning.

I can identify the particular shade of the altar-cover as white, cream-colored or beige, but because I’m not a perfume maker or sommelier, I lack the same vocabulary for the incense the priest is burning.

When trying to describe it, I fall back on generalizations: sweet, musky, church-y.

Because humans generally cannot label, intellectualize and analyze odors to the same degree as sights or sounds, Dalton argues what we’re left with is emotion.

“I think somehow being able to describe something very specifically may remove some of the aura of emotion from it,” Dalton said.

Because I don’t know what kind of incense my priest burns at the altar, I don’t file it away in my brain as ‘myrrh’ or ‘frankincense,’ but simply ‘Christmas’.

“When we smell an odor, rather than labeling it as the odor of something, very often, it just becomes associated to the context that we’re in at the time,” Dalton said.

Retailers use scent to draw shoppers in

Retailers capitalize on the contextual connection between smell and place to draw people into their stores.

ScentAir, a marketing firm that designs signature scents for businesses in more than 100 countries, said many of its retail clients switch to holiday aromas this time of year.

“As an example, let me take one of the very popular holiday scents that we use called holiday spice,” said ScentAir CEO Andy Kindfuller.

The scent incorporates notes of pine needles, cinnamon, berries and orange. With it, and other holiday scents, Kindfuller said retailers aim to create new memories of shopping to draw people back to brick-and-mortar stores in an age of online retail.

The scent also brings shopper back to happy holiday memories of the past.

“It brings back to the consumer memories that they have, maybe from their childhood where they were around pine needles or were eating oranges and berries at the holiday time, and those memories come back to them and again makes them feel better about that retailer,” Kindfuller said.

One client, a major clothing retailer, started using a woodsy pine scent in early November to remind people to start their Christmas shopping.

Scent memories are fragile, though. Over-exposure can reduce the emotional punch, which is why not many people have powerful holiday memories associated with common smells, like coffee. And why Lou McCall, who sells trees at Philadelphia’s Christmas Village, doesn’t think ‘Christmas’ anymore when he smells evergreens.

“I have absolutely been desensitized. I don’t even know what a Christmas tree smells like anymore,” McCall said. “I lift so many of these and I’ve been doing it for a couple years, if anything, whatever the tree smell may be, it just smells like work.”